The present invention relates generally to the manufacture of signs such as exit signs illuminated by selected light sources and having a standard housing frame forming a basic housing unit. The present invention particularly relates to molds for stepwise molding, using two different plastics, signage composed of a plurality of symbols surrounded by a continuous matrix adapted for coupling to the basic housing unit.
Emergency lighting fixtures exist, such as those disclosed in U.S. Pat. No. 6,152,581, that use a variety of light sources for internal illumination and use a variety of power sources for powering the light sources. Many emergency lighting fixtures share a housing of common design, and particularly a housing frame of common design, which is preferably molded either as a single, unitary element. The housing typically has at least certain structural elements that are useful in some if not all of the fixtures. The housing frame forms a basic element to which one or more facing plates that include exit message indicia can be coupled. The housing frames are preferably formed of a polymeric material such as ABS blended with polycarbonate. The same materials can be used for a continuous matrix portion of the facing plate while openings are provided in the continuous matrix defining the exit message.
To ensure that the exit message indicia are easily seen, a planar sheet or plate is mounted to the interior surface of the facing plate. The interior sheet or plate is made of a different plastic that is generally transparent or translucent and colored a suitable eye-catching color. The term “different plastics” is intended to cover plastics of differing composition as well as plastics of substantially the same composition having merely a difference in appearance. Back illumination of the facing plate creates a colored image showing through openings in the facing plate that are shaped in the form of the indicia. The sheet or plate of colored plastic is generally hand assembled to the facing plate inner surface prior to assembly of the facing plate to the housing frame. Increased use of moldable fastening elements has eliminated the need for separate fasteners such as screws or the like in the assembly and mounting of the fixtures. In particular, snap-fitting structural elements formed integrally with the facing plates provide easy snap-fitting of the colored plastic sheets or plates to the interior of the facing plates. Further snap-fitting structural elements formed integrally with either the facing plates or the housing frames allow coupling of the facing plates to the housing frames to form the primary structural housings of the fixtures. Other snap-fitting structural elements can be used for mounting of lamps, circuit-bearing platforms, wiring and the like. Assembly of such fixtures is facilitated at least in part due to a reduced number of parts occasioned by the integral nature of the housing frames. However, the illumination provided to the indicia through the colored plate is not always satisfactory, particularly with low-level light sources.
What is needed is an improvement in the delivery of illumination through the indicia defining openings in the facing plate. What is further needed is any possible reduction in cost and assembly time through the elimination of further hand assembly steps in the formation of the lighted emergency exit signage.